The present invention relates generally to filter material for removing contaminants from air or other fluid streams. More particularly, the present invention relates to a filter material formed of an open-pore foam support body having sorptive particles bonded to the surface of the open pores of the foam support body.
Filter materials formed of a porous substrate containing particulate material are well known in the art. For example, U.S. Pat. No. 3,238,056 to Pall et al discloses a filter material comprising a porous material substrate, having a proportion of pores ranging from greater than 25 microns up to about 150 microns in diameter, whose filtration characteristics are modified by impregnating the pores of the substrate with particulate material in an amount to reduce the pore diameter to less than 25 microns. The particulate material is deposited in the pores of the substrate by contacting the substrate with a fluid slurry of particulate material composed of a mixture at least 5% fibrous material, and preferably at least 25% of fibrous material, and nonfibrous particulate material. Pall et al disclose that any porous material whose pores extend from surface to surface may be used, including polyurethane and other forms, although the disclosed process is stated to be particularly useful for upgrading coarse filter media such as papers and nonwoven fibrous bats. Although Pall et al disclose that particulate material of any type may be used, including activated carbon as the nonfibrous particulate material, the preferred particulate material is composed of glass fiber as the fibrous component and diatomaceous earth of nonfibrous component.
U.S. Pat. No. 3,865,758 to Yoshida et al discloses a method of producing a polyurethane foam filter material containing an activated carbon adsorbent. According to the disclosed process, particles of activated carbon are precoated with a solid film of a selected polymeric material. A polyurethane foam-forming composition comprising isocyanates and polyesters and polyethers is reacted in the presence of the coated particles of activated carbon absorbent to form a foam filter material. The film of polymeric material coating the activated carbon particles may be removed after the formation of the foamed product by treating the foamed product with a solvent which dissolves the polymeric coating on the activated carbon material, but does not substantially dissolve the resultant polyurethane foam. If necessary, excess solvent may be removed by washing or other conventional practices and thermally drying the polyurethane foam filter material.
U.S. Pat. No. 4,800,190 to Smolik discloses a process for the production of a filter material comprising an open-pore foam carrier having absorbent particles of different sizes fixed on the foam carrier and in the open pores thereof. According to the disclosed process, after a layer of adhesive, such as modified acrylates, polyurethanes, silicone rubber, polyvisylidene, polyvinyl chloride, polyamide and polyester granules and powders, is applied to the pores of the open-pore foam carrier by impregnating the foam carrier with the adhesive, the first relatively larger absorbent particles are applied to the foam carrier and introduced into the open pores thereof and thereafter, prior to the adhesive setting, the second relatively smaller absorbent particles are applied to the foam carrier and introduced into the open pores thereof. Thereafter, the foam carrier is passed through a drying apparatus at temperatures of around 150.degree. C. and those absorbent particles which are not fixed on the foam carrier or in the pores thereof are removed by suction.